The Australian national differential RTP grid

Over the last 50 years total magnetic intensity (TMI) has been the most measured expression of the magnetic field, not for interpretational advantage but for practical and cost-effective acquisition. Since 2011, Geoscience Australia has produced a series of national TMI compilations from a minimum of 795 individual survey grids. TMI measurements are (except in regions of intense local fields) the scalar magnitude of the vector component parallel to the local geomagnetic field. There is significant variation in direction of the magnetic field across Australia, and therefore the nature of TMI also varies considerably. The shallowest geomagnetic inclination of -40° at the north coast of Queensland and the Northern Territory (Figure 1) is steeper than would normally be expected at those latitudes, and is associated with a substantial northward departure of the geomagnetic equator (the line of zero inclination) through the South China Sea. The steepest inclination of -70° is at the south coast and in Tasmania (Figure 1).